Factors affecting starch digestibility rate of maize grain in poultry

Maize, the most common energy feed ingredient in poultry diets, has a high starch proportion in the grain endosperm, ranging from 65 to 75% in various hybrids. The rate and extent of digestion are major determinants of maize starch nutritive value. Starch digestion follows the first-order kinetics, and according to the digestibility kinetics, starch can be divided into rapidly digestible (RDS), slowly digestible (SDS), and resistant starch (RS). Different intrinsic and extrinsic features of maize grain affect the rate and extent of starch digestibility. Differences in starch granule composition, such as amylose-to-amylopectin ratio, crystallisation, association with lipids and zeins, as well as shape, size and presence of surface pores affect starch digestibility kinetics. More so, an important factor affecting digestion is grain processing. Particle size affects feed intake, the passage of bolus and susceptibility to enzyme-starch binding, while hydrothermal processing leads to starch gelatinisation. However, too high temperatures can lead to RS formation. This review summarises the available literature data on factors identified as crucial in the digestibility kinetics of maize starch.